Over recent years, research and development of light-emitting diodes (hereinafter referred as to “LEDs”) have been advancing at a rapid pace, with various types of LEDs being developed, productized, and used in a wide range of fields. Due to their features of low power consumption, long life, and compactness, LEDs have long been used as operation indicator lights for electronic equipment and the like. These LEDs have been much used in, for example, backlights for liquid crystal panels, various kinds of display boards, electronic signboards, decorative illumination devices and so forth, and have now come to be used in the field of illumination. In the illumination field, they are used for automobile headlights and taillights, in planar illumination devices incorporating a plurality of LEDs, in illumination devices that incorporate LEDs inside a tube and can be used in the same manner as fluorescent tubes, for example.
The planar light sources that are used for indoor illumination devices and the like are required to emit light uniformly, but since LEDs have strong light directionality, they are not suitable, without modification, to be used for indoor illumination devices. Accordingly, as light source devices using a related-art LED that are for obtaining illuminating light with planar, uniform illuminance distribution, light source devices in which reflection means is provided on the emitting surface of light so that the light is multiply reflected are well known (see Patent Documents 1 and 2 below). The strong-directionality light of LEDs causes unpleasant brightness called “glare” when it enters eyes directly. Light source devices that, in order to prevent this glare, are designed so that the light emitted from the light source is reflected once or more times at the sidewall of the aperture of reflection means provided inside the light source device or on its reflection surface to pass through the aperture are well known (see Patent Document 1 below).
In the light source device set forth in Patent Document 3, a point light source is provided in the bottom of a containing assembly called a casing or housing, and reflection means is provided at the mouth portion of the casing, or more precisely on the surface that faces the point light source, so that the strong-directionality light from the point light source is multiply reflected and uniformized to be emitted. In order to heighten the light utilization rate in the light source device, the casing and the reflection means have inner wall surfaces that are formed from material that has high light reflectivity, low light transmissivity, and low light absorptance. As such material, ultrafinely foamed reflection plate is used. Ultrafinely foamed reflection plate is a material that has, for example, 98% light reflectivity, and 1% each of light transmissivity and light absorptance, and is lightweight and easy to process. With this ultrafinely foamed reflection plate, the casing and reflection means, for example, can be fabricated with ease.